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INTRODUCTION to JAVA Java was conceived by James Gosling, Patrick
Naughton, Chris Warth, Ed Frank, and MikeSheridan at Sun Microsystems, Inc. in 1991name with Oak
In 1992 this can be used in hand held devices
1993 this cab be used in WWW applications
the same team in 1994 Hotjava bower isdeveloped ,it is more popular internet users.
This language was initially called Oak but wasrenamed Java in 1995
1996 java itself established not only internet
program but also general purpose, and OOPlanguages.
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The Bytecode
Bytecode is a highly optimized set ofinstructions designed to be executedby the Java run-time system, which is
called theJava Virtual Machine (JVM). That is, in its standard form, the JVM
is an interpreter for bytecode. This
may come as a bit ofa surprise
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Java Features
Simple Secure
Portable
Object-oriented
Robust
Multithreaded Architecture-neutral
Interpreted
Hi h erformance
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SimpleJava is simple because there are
various features that makes the java
as a simple language. Programs are
easy to write and debug because
java does not use the pointers
explicitly, operator overloading ,multiple inheritance, process header
files, goto stement
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Object-OrientedTo be an Object Oriented language, any
language must follow at least the four
characteristics.
Inheritance
Encapsulation
Polymorphism
Dynamic binding
R
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Ro ust
Java is a strictly typed language, it
checks your code at compile time.
Java has the strong memory
allocation and automatic garbage
collection mechanism.
It provides the powerful exception
handling and type checking
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Multithreaded Multi thread means handling multiple
tasks simultaneously
Java supports multithreaded
programming, which allows you to
write programs that do many things
simultaneously.
Java is also a Multithreaded
programming language.
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Architecture-Neutral One of the main problems facing
programmers is that no guaranteeexists that if you write a programtoday, it will run tomorroweven on
the same machine Operating system upgrades,
processor upgrades, and changes in
core system resources can allcombine to make a programmalfunction
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The Java compiler does this by
generating byte code instructions, to
be easily interpreted on any machine
and to be easily translated intonative machine code
The compiler generates an
architecture-neutral object file format
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Interpreted and HighPerformance
Java enables the creation ofcross-platform programs by compiling intoan intermediate representation called
Java bytecode. This code can beinterpreted on any system thatprovides a Java Virtual Machine
Other interpreted systems, such asBASIC, Tcl, and PERL, suffer fromalmost insoluble performance deficits.
Java, however, was designed to-
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Distributed
Java is designed for the distributedenvironment of the Internet, becauseit handles TCP/IP protocols, HTTP and
FTP are developed in java In fact, accessing a resource using a
URL is not much different from
accessing a file. Internet programmers can call
functions on these protocols and can
get access the files from any remote
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Dynamic Dynamic Java programs carry with
them substantial amounts of run-time type information that is used toverify and resolve accesses to
objects at run time.This makes it possible to dynamically
link code in a safe and expedient
manner.Java is capable of dynamically linking
in new class libries, methods and
objects.
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Portability
The feature Write-once-run-anywhere makes the javalanguage portable provided that the system must haveinterpreter for the JVM.
programs to be dynamically downloaded
to all the various types of platformsconnected to the Internet, some means ofgenerating portable executable code isneeded.
the same mechanism that helps ensuresecurity also helps create portability
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Security
Java system verify all memory accessbut also ensure that no virus are
communicated with appletJava achieves this protection by
confining a Java program to the Java
execution environment and notallowing it access to other parts of thecomputer.
The absence of pointers that
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Java environment
JDK (java development KIT)collection of tools
Appletviewer ( java compatiblebrowser)
Javac ( compiler)
Java (interpreter)Javap( dis assembler) : convert the
bytcode to program
Javah : produces the header files for
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JAVA API Language support package
Utilities package
Input /Out package
Networking package AWT package
Applet package
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Data Types, Variables,and Arrays
Integers This group includes byte,short, int, and long, which are forwhole valued signed numbers.
Floating-point numbersThis groupincludes float and double, whichrepresent numbers with fractional
precision.
Characters This group includes char,which represents symbols in a
character set, like letters and numbers.
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Integers
long 64 9,223,372,036,854,775,808 to
9,223,372,036,854,775,807
int 32 2,147,483,648 to2,147,483,647
short 16 32,768 to 32,767
byte 8 128 to 127
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Floating-Point Types
Double 64 4.9e324 to1.8e+308
float 32 1.4e045 to 3.4e+038
Literals
Integer Literals
Floating-Point Literals
Boolean Literals
Ch t E
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Character EscapeSequences
Escape Sequence Description \ddd Octal character (ddd)
\uxxxx Hexadecimal UNICODE
character (xxxx) \ Single quote
\ Double quote
\\ Backslash
\r Carriage return
\n New line (also known as line
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VariablesThe variable is the basic unit of
storage in a Java program. A variableis defined by the combination of anidentifier, a type, and an optional
initializer. In addition, all variables have a
scope, which defines their visibility,
and a lifetime Declaring a Variable
type identifier[ = value][, identifier [=
value] ...] ;
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Arrays
One-Dimensional Arrays type var-name[ ];
int month_days[];
int month_days[] = { 31, 28, 31, 30,31, 30, 31, 31, 30, 31, 30, 31 };
Multidimensional Arrays
int twoD[][] = new int[4][5];
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Sample program
/*
This is a simple Java program.
Call this file "Example.java". */
import java.io.*;
import java.util.*;
class Example {
// Your program begins with a call to
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Progrm-ii
import java.io.*;
import java.util.*;
class Example2 {
public static void main(String args[]) {
int num; // this declares a variablecalled num
num = 100; // this assigns num the
value 100
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Using arrays
class Average {
public static void main(String args[]){
double nums[] = {10.1, 11.2, 12.3,13.4, 14.5};
double result = 0; int i;
for(i=0; i
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Two dimensional arrays
class TwoDArray {
public static voidmain(String args[]) {
int twoD[][]= newint[4][5];
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